Understanding Trisomy 18: Risk Assessment & Next Steps

Question
Hello Doctor,

I am 31, have a 5 year old daughter (tomorrow! :) and my last period started on November 12th.  Here is my concern and question for you:  I did the Quad test on Tuesday and the nurse called me yesterday to say that although my Downs (1 in 3000) and Spinal Bifida (1 in 10,000) looked great my results for Trysomy 18 came back "off" for my age - 1 in 22.  Of course with this being a fatal disease I am scared.  What should my results have been for my age to keep me "normal" and is there still a really good chance my baby is fine?  I am going for a level 2 and will do an amnio if necessary, but could use some reassurance if it's out there.

Thank you!


Answer
At the age of 31, your risk of Trisomy 18 should be greater than 1 in 2700. If it was 1 in 22, it appears to be abnormal. I would recommend an amnio to be absolutely sure. Of course, Trisomy 18 usdally ends up in a miscarriage. HOwever, for peace of mind, I would have an amnio. I do not think that a level II sonogram will show any chromosomal defects.